Protect Horses Against Potomac Horse Fever

Protect Horses Against Potomac Horse Fever

PHF is most commonly found near creeks and rivers and likely caused when horses ingest infected aquatic insects such as damselflies, caddisflies, and mayflies.

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This summer, several cases of Potomac horse fever (PHF) were reported in central Virginia. Although the disease is not contagious, it can be fatal and the Virginia Department of Agriculture and Consumer Services made horse owners aware of the threat.

Megan Green, DVM, manager of Merial’s Large Animal Veterinary Services, advises horse owners, especially those in geographic areas where PHF is prevalent, to consult with their veterinarians.

“(Your veterinarian) will have the latest information about the cases in the surrounding community and help assess the situation,” Green says. “But since there have been cases reported, it’s very likely he or she will recommend vaccinating. It’s the only way to help protect horses against Potomac horse fever.”

PHF is most commonly found near creeks and rivers and likely caused when horses ingest infected aquatic insects such as damselflies, caddisflies, and mayflies. Named PHF because the initial 1979 outbreak occurred near the Potomac River in Maryland, the disease has since been identified in 43 states, three Canadian provinces, parts of South America, the Netherlands, and France.

In determining a horse’s possible exposure to PHF, owners should consider the horse’s immediate surroundings and the local projections for this year’s aquatic insect population. In the case of central Virginia, Michael Erskine, DVM, Dipl. ABVP, interim director of the Virginia-Maryland Regional College of Veterinary Medicine, says the recent heavy rainfall could have contributed to the increase in the number of disease carriers.

PHF can have serious complications, so the decision about whether or not to vaccinate is an important one. The fatality rate in untreated cases can be up to 30%. Another devastating effect of PHF is the possible development of laminitis, which occurs in up to 40% of affected horses.

Green cautions horse owners to be vigilant as the disease is difficult to diagnose and has clinical signs that are subtle and mimic other diseases.

“Early detection is key to potential recovery,” she says. “Signs at the disease’s onset include fever ranging from 102-107°F, decreased intestinal sounds, and diarrhea. As the disease progresses, some horses suffer from toxemia and dehydration.”

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